Vortex Deconfinement in the Two Dimensional XY Model

摘要

Tunneling experiments on double layer quantum Hall systems exhibit a zerobias conductance resonance akin to the Josephson effect. The excitations responsible fordissipation in this resonance have not been identified. We analyze a model believed to describethis system, the two-dimensional XY model in a magnetic field. This system supports vortexexcitations, which in the quantum Hall realization represent charged quasiparticles. A singlesuch pair is connected by a string of overturned spins, leading to linear confinement. Weshow that this system supports two transitions, one in which closed strings proliferate, and asecond in which vortices unbind. The transitions are shown to be dual to one another, and areremarkably continuous. The existence of string excitations may explain the anomalously largedissipation seen in the interlayer tunneling experiments.